1. Field of the Invention
The present invention relates generally to the treatment of wastewater and particularly to a method for the conventional treatment of wastewater during periods of cold air temperature utilizing the controllable recirculation of air through the filter medium.
2. Description of the Prior Art:
The use of trickling filters for treatment of wastewater is well known and practiced in the prior art. Conventional filters typically utilize a rock filtering medium of circular design with a rotary distributor overhead applying wastewater to the surface of the rock. Filters of this design normally are economical in construction and operation and have had wide commercial acceptance. However, in recent years, in response to increased environmental concern, the discharge from wastewater treatment plants is now required to be of a quality that will allow minimum water quality standards as established by state and federal laws to be met in the receiving stream. In order for this to be accomplished, the output from the trickling filter must meet established parameters.
Biological life within the filter medium is the active agent for the treatment of the wastewater, however, its efficiency is temperature dependent. Thus, as the ambient air temperature falls, as occurs in fall and winter, so does the efficiency of the treatment process. This is a very undesirable situation and one which presently is intolerable.
In conventional operation, during cold weather, wastewater is warmer than the atmospheric air above the filtering medium and when distributed over the filtering medium, warms the air in the voids in the medium, creating an upward air flow. Unfortunately, the downward flow of wastewater creats a downward air flow and the end result is a potential stagnation of air flow through the filtering medium. Further, during seasonal climatic changes when the temperature differential between the ambient air and wastewater is small, minimal air flow through the filtering medium occurs. Thus frequently, the filter medium is subjected to minimal ventilation resulting in insufficient oxygen and temperature to sustain the biological life for the metabolism of the pollutants within the wastewater.